If you want to lose 4 kg in a week it will definitely come back. Your weight will just go up and down forever. The best way to lose weight is just to eat healthy, drink a lot of water and work out. For a lasting result you should lift weights, don't eat junkfood, snacks, but just eat healtier, for example fruit, vegetables, eggs low fat quark etc. Good luck.
Never start any diet program before consulting with your Doctor